Response of sucrose metabolizing enzyme activity to CPPU and p-CPA treatments in excised discs of muskmelon

We investigated the effects of 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU) and para-chlorophenoxyacetic acid (p-CPA) treatments on the sucrose metabolism-related enzyme activities in excised mesocarp discs of muskmelon fruit at different growth stages. Both a CPPU and a p-CPA treatment applied to discs prepared at 5 and at 20 days after anthesis (DAA) increased acid invertase (AI) activity and neutral invertase (NI) activity, but neither treatment affected these activities in the discs prepared at 45 DAA. Both plant growth substances increased the activity of sucrose phosphate synthase (SPS) in the discs at 5 and 20 DAA, but neither affected it in the 45 DAA discs. The sucrose synthase (SS) activity was markedly increased by p-CPA treatment in the 20 and 45 DAA discs, but was not affected at 5 DAA. CPPU treatment did not activate SS of discs throughout the growth stage.